Kidney transplantation's considerable benefit is offset by the infectious and metabolic morbidity related to its required immunosuppressive drugs. Recently, belatacept, a CD28-B7 costimulation pathway inhibitor, has been approved for use with substantial evidence suggesting that it can prevent kidney rejection with less morbidity, and perhaps serve as a centerpiece agent for tolerance regimens. However, although belatacept appears to control naive immune responses well and evoke few off-target side effects, its control of memory T cell (TM) responses is less robust than hoped and its use is associated with significant morbidity related to the Epstein-Barr Virus (EBV). This Project will leverage substantial investigator experience and extensive preliminary data to develop logical adjuvant therapies that can be paired with belatacept. In particular, it will study altered integrin adhesion molecule expression as a means of identifying TMS with potential to cause belatacept-resistant rejection, and test four novel biologic agents for their ability to improve belatacept's antirejection effect in a rhesus monkey model of kidney transplantation without evoking the side effects related to existing standard immunosuppressive drugs. The ultimate goal is to develop one or more translatable regimens that can mediate lasting, well-tolerated, antigen-specific immune modulation to prevent allograft rejection. There are 3 Specific Aims. 1) To determine the effects of leukocyte function antigen (LFA)-Idirected therapy as an adjuvant to belatacept-based maintenance immunosuppression. We will test two novel LFA-1-specific monoclonal antibodies (Mabs) with identical specificity but distinct isotype, loGI or lgG4, for their efficacy in preventing belatacept-resistant rejection, and assess their effect on protective immunity, particularly toward the EBV-homologue, lymphocryptovirus (LCV). 2) To determine the role of an activation-induced LFA-1 conformational modification in mediating rejection and test the novel conformation specific, anti-LFA-1 Mab, AL-57. as an adjuvant to belatacept. We will define the AL-57 epitope in rhesus alio- and viral-specific immunity and test AL-57 for its ability to prevent or reverse rejection. 3) To define the effects of very late antigen (VLA)-4-specific therapy as an adjuvant to belatacept. We will test the VLA-4- specific Mab natalizumab for its efficacy in preventing or reversing belatacept-resistant rejection, and assess its effect on protective immunity. From these studies we will examine new approaches toward immunosuppression, using translatable agents in a clinically relevant pre-clinical model while concurrently providing new insights into the role of integrins in viral- and allo-immunity.